1. Field of the Invention
The present invention relates to an engine intake control system comprising: an intake passage body attached to an engine; a first intake passage formed in the intake passage body and having a downstream end connected to an intake port of the engine; a second intake passage also formed in the intake passage body and having a downstream end connected to the intake port; and a changeover valve that includes a valve shaft rotatably supported by the intake passage body, and a valve plate attached to the valve shaft, the valve plate being moved rotationally, by a rotational movement of the valve shaft, between a first changeover position, where the valve plate closes the second intake passage and allows the first intake passage to be connected to the intake port for air flow, and a second changeover position, where the valve plate closes the first intake passage and allows the second intake passage to be connected to the intake port for air flow.
2. Description of the Related Art
The above-mentioned engine intake control system has been known by the disclosure of Japanese Patent Application Laid-open No. 2000-234522.
The engine intake control system disclosed in the above-mentioned document employs a changeover valve that includes a valve shaft and a valve plate. The valve plate is attached to the valve shaft and extends in the direction of only one side of the valve shaft. In other words, the valve plate is cantilevered. A moment of a constant direction caused by the intake negative pressure acts on the valve plate irrespective of whether the valve plate is positioned at a first changeover position or a second changeover position. Operating the valve plate to change its positions against the above-mentioned moment needs a large power, so does keeping the valve plate at a predetermined changeover position against the moment.